Aimo Johannes Lahti’s remarkable semiautomatic shoulder cannon made it into the first phase of tiny Finland’s “Winter War” against Soviet invaders in 1939-40, but just barely. According to Finnish arms historians, only two prototype guns, in 20x113mm Lahti caliber, were available to be pressed into action. However, this mighty duo, manned by stalwart gunners of Infantry Regiment 28, soon scored several kills on light tanks at up to 400 meters in bitter fighting in the area around Lake Lagoda.

This first blood validated Lahti’s outspoken rejection of smaller calibers and his years of steadfast endorsement of 20mm loadings for the job of a man-portable tank buster. The relatively light and highly portable gun - hastily but ingeniously crafted from his already successful 20mm aircraft cannon - was doing a job for front line infantrymen that no other native design could match.

Although the Red Army got its frozen butts thoroughly kicked this first year, the second phase, known as the “Continuation War” dragged on in fits and starts until 1944. During this time some 1,850 production version L-39 guns were built in Jyaskyla at Valtion Kivaaritehdas, the state rifle factory, sent to the front lines as fast as they could be assembled. These were chambered for the more commonly available Solothurn 20x138B (aka 20mm Breda) round, already in service and high production with Germany, Finland’s ally of necessity against Soviet dictator Josef Stalin.

Although capable of punching through more than a 1/2-inch of 60-degree inclined armor plate at a respectable 500 meters, the new guns were admittedly no match for the heavily armored T-34, considered by many experts to be the best medium tank in World War II. Even so, the big Lahti was bad news for lighter armored vehicles.

Bunker busting was another virtue where accuracy, range and optional HE (high explosive) projectiles were used to devastating effect through firing apertures. Also, Red Army snipers, armed with 7.62x54R Mosin-Nagant rifles and usually operating well within 900 meters of Finn lines, were spectacularly dealt with by 20mm HE shells from L-39s safely positioned 1,000 or more meters away.

Smoking the Bear

Interestingly, it is also reported to have been useful as an incendiary weapon in the short but often bone dry Finnish summer. A crude but effective indirect fire method was utilized to get quadrant elevation of +32 degrees for maximum range of about 7,000 meters. Special phosphorus loads were developed with a duplex booster impact fuze that energetically blasted a rain of fire on contact with treetops as the round plunged down into the target area. Resultant wildfires - beginning way above ground thus nearly impossible to extinguish - made life in Red Army rear areas a literally hellish inferno.

Although of limited effectiveness against conventional Russian medium and heavy tanks, the L-39 proved effective in discouraging low level bombing and strafing aircraft. It was found to be particularly useful against the notorious Ilyusin 2 “Schturmovik” (ground attack aircraft) with its pilot well protected inside an armored bathtub of steel plates up to 12 mm (almost 1/2-inch) thick. Adding insult to injury, the Il-2 was armed with both 7.62x54R machine guns and a pair of its own 20mm auto cannons.

Dubbed the “Flying Tank” by Russkis, the Schturmovik was able to withstand repeated hits by ordinary small arms fire including .50 caliber. But not 20mm rounds from the L-39, often delivered as Finnish gun writer P.K. Kekkonen colorfully writes, “at shooting range similar to that of duck hunting with a shotgun.”

Full-Auto Follies

The L-39’s effectiveness in the AA (antiaircraft) role was limited by semiautomatic function so conversion to full-auto was a logical goal. Unfortunately, the immutable laws of physics spoiled the intended benefits of this. According to Kekkonen, the first conversions were field expedients made by removing the sear and using the bolt release lever (lower portion of the pistol grip assembly) as a trigger. This reportedly produced the desired effect of full-auto at about 400 rpm.

One supposes that, since these guns were more or less securely anchored to tree stumps using a cleverly improvised “birdcage” mount, the gun’s considerable recoil - intensified at nearly 7 rounds per second - was dampened to levels at least tolerable to human gunners. However, the receiver wasn’t afforded this same benefit.

Aimo Lahti’s very efficient design for 20mm semiautomatic fire in a relatively light weapon was violated by the inevitable stress and pounding of full-auto, resulting in receiver cracks and maybe even instances of catastrophic failure. Wartime priorities must have overruled these shortcomings and factory-built selective-fire versions were fielded in the summer of 1944. Designated as L-39/44, more than 300 of these monster machine rifles entered service, specially fitted with AA sights and improved tree stump mount featuring beefy recoil damping springs.

The Finns are known to be a practical people so the very serviceable Lahti 20mm was not discarded in the postwar/Cold War years when probable employment of the 39/44 as an anti-helicopter weapon made a lot of sense. Some 645 guns were maintained in reserve stocks until 1986 when the decision was made to donate some to museums and deactivate the rest for sale to private collectors in Finland.

“Man-Eating Jackrabbits”

Now, it may be fair to ask what happened to all those other guns left over from more than 2,000 produced in World War II. Well, some were lost in combat of course, but 1000 perfectly good and fully functional semiautomatics were put on the world surplus market around 1960. 200,000 rounds of ammo went too, just in case big bore plinkers wanted to test fire their new shoulder cannons.

It looks like most of this offering was snapped up by Interarmco’s redoubtable Sam Cummings who soon found lots of willing buyers among America’s military gun collectors and enthusiasts. Potomac Arms in Virginia and Seaport Traders in California were both retail and mail order outlets for Interarmco, offering mint condition Lahti’s with every accessory and tool imaginable for the astonishingly low price of $99.95! Need ammo? How about 100 rounds of AP-T for a mere 85 cents each?

Well, more than forty years later one can expect that prices have gone up a little. A quick internet check pulled up the Ohio Arms website, offering your choice between two L-39s at an average price of $8,000. Ammo? Yeah, but the buck a round days are long gone....

Roll Your Own

Cannon shooters of all stripes tend to be a resourceful bunch and enthusiasts have a good selection of sources for components and technical data. If you are looking for a relatively economical way to feed your Lahti or other 20mm rifle, some prominent dealers are:

Big Sky Surplus in Spokane, WA (www.bigskusurplus.com)

Old Western Scrounger in Montague, CA (www.ows-ammunition.com)

River Valley Ordnance in Harvester, MO (www.rvow.com)

Find Out More

As might be supposed, Finland is the best place to get information on all aspects of Aimo Lahti’s remarkable gun designs. The internet has shrunk the world to the point where L-39 information in English from experts in this small but proud and fiercely independent country is only a few mouse clicks away:

More old-fashioned researchers are urged to find a copy of Markku Palokangas’ excellent 1991 book Military Small Arms in Finland, Vol 2.

Ian Hogg’s very comprehensive Encyclopedia of Infantry Weapons of WWII may be more readily available, with a big section on A-T rifles and related weaponry.

If you are lucky enough to have access to back issues of SMALL ARMS REVIEW’s predecessor, MACHINE GUN NEWS, you must look up Eric Williams’ authoritative and in depth two-parter on all things 20mm, published in July and August 1993. Carl Silver followed this with some more good L-39 stuff in the October 1995 issue.

Tom Ring’s Lahti

The gun featured here in live fire was purchased by Tom Ring in 1991 for the then-princely sum of $2750, in a deal brokered by Old Western Scrounger. No, he says, it is not for sale.

OWS also has been Tom’s primary source for reloading tools and components, notably the “Rock Crusher” press. He rolls his own in various forms and, as a graduate of the prestigious Colorado School of Trades Gunsmithing Course, is quite knowledgeable on all aspects of the Lahti and its ammo. Oh, and I ought to mentioned that he spent a very interesting and productive time with INTERARMS as their Chief Warranty Gunsmith.

Somewhere along the way the L-39’s original owner had parted with most of those great accessories and tools that were so thoughtfully included back in the early 1960’s when Sam Cummings was selling them via mail order. But not long afterward, as luck would have it, Tom - a former Marine Embassy Guard - got a job in Finland for a not-to-be-named government contractor. This gave him a year to develop many friends and contacts among the Finnish gun community and he acquired a full set of necessary and desirable whatnots for his L-39.

Among these friends is Seppo Kinnunen who, along with gun writer Markku Palokangas, was instrumental in providing the archive photos that accompany this feature and in pointing me toward other authoritative sources in Finland for historical and technical info. Thanks guys!

Ski Silliness

The L-39’s highly unusual combo bipod and skid mount has given rise to a persistent myth that begs for debunking. No, the “skis” are not for pulling the gun through the snow behind reindeer drafted into Finnish Army service. They are far too small to develop sufficient “float” to keep the heavy gun from burrowing into any snowfall deeper than a couple of inches. When this becomes necessary, a “pulk” (sort of a shallow snow canoe) is used to haul the gun, ammo, and assorted stuff.

Instead, the mini-ski skids on the mount are used to facilitate dragging the gun for short distances over dirt as the crewmen crawl forward (or withdraw from) front line positions under enemy observation. A pair of special towropes, thoughtfully included in the accessory chest, are specifically provided for this purpose, and snap into thick eyelets on the folded up bipod.

Once into a suitable firing position offering cover and concealment, the crewmen lower the hefty bipod feet into the dirt, raising the gun a couple of inches above the skids. This gives a very stable shooting platform and offers an important additional benefit as well.

Kick Crock

It would seem that similar misinformation is routinely spread by a few overly dramatic scribes and some backyard big bore blasters in describing the L-39’s allegedly snot-kicking recoil. Yes, the potent 20mm load naturally generates awesome forces in the equation of Newton’s Third Law of Motion, but Lahti was a clever guy and built in several things to bring this to tolerable balance.

First, the bipod legs should be firmly planted in the ground. This anchors the gun and allows the two small shock absorbers under the receiver at the mount point to absorb some of the firing stress on the receiver (so that it needn’t be even thicker and heavier) and on the gunner. Then, the muzzle brake takes care of about 40% of kick, and semiautomatic cycling of the massive bolt and associated parts cuts out another 20% or so.

Finally, the gunner must press his shoulder firmly into the gun’s generously padded and well-shaped buttplate, pulling forward with both arms just before each shot. This melds man and machine, delivering what Ring describes as, “more of a hefty shove than a kick.”